A variety of consumer products are packaged using a sealing machine, such as a horizontal form, fill and seal machine. Typically, a web of heat sealable thermoplastic film is moved downstream and is continuously formed around the products or articles being packaged. The tubular web and the articles then move to a sealing die which seals and severs the tubular web between the articles to provide individual sealed packages.
One of the earliest known sealing machines was developed in the late 1940's by Sam Campbell of the Hudson Sharp Company, of Green Bay, Wis. The machine, which became known in the industry as the "Campbell Wrapper," included a product in-feed conveyer, a horizontal forming shoulder for enveloping the product within a wrapping material, a rotary back-seam sealing device which acted as the prime mover for the wrapping material and horizontally rotating sealing bars which both sealed and cut the wrapping material. The Campbell Wrapper was designed for high-speed overwrapping of candy bars and the like.
The most critical element of any horizontal form, fill and seal machine is the sealing station because the articles must be effectively sealed in a package which 1) will not inadvertently open, 2) is structurally sound and 3) has all of the exterior graphics properly aligned and displayed thereon. In order to form a reliable heat seal using thermoplastic film, it is necessary to closely monitor and control three critical parameters during the sealing process, namely the amount of time the sealing die is closed over the material (hereinafter referred to as "dwell time"), the temperature of the die while sealing the material, and the pressure exerted by the die when compressing the material. The time, temperature and pressure parameters are highly interdependent so that if one of the parameters is lowered, one or more of the other parameters must be elevated. For example, if the dwell time is lowered to improve production rates, the temperature of and/or pressure exerted by the die must be increased.
The time, temperature and pressure parameters must also be elevated if the thickness of the material being sealed increases. Typically, the thickness of the material being sealed can vary widely from one seal to the next. This wide variation occurs because present sealing systems are incapable of positively controlling the exact location of the wrapping material during the sealing process including the alignment of tucks or folds in the package in relation to the position of the seals. As a result, excessive wrinkling or crumpling of the material may occur around some of the seals. The extra wrinkles make the material being sealed thicker and extra time, temperature or pressure must be used to properly seal the thicker material. Accordingly, either the sealing time, sealing temperature or sealing pressure must be elevated above normal levels in order to account for the wide variation in the thickness of the material which generally results in reduced production rates and/or wasting valuable resources.
U.S. Pat. No. 5,094,657 discloses one method and apparatus for maintaining better control of the wrapping material. After a low density polyethylene bag has been partially formed to provide pouches, a constant air flow is provided from an air manifold to keep the pouches open as they move downstream on a conveyor belt. The conveyor belt includes vacuum holes which pull on first sidewalls of the pouches while the constant airflow from the air manifold lifts second sidewalls thereof. The vacuum in the conveyor belt and the air manifold cooperatively open the sidewalls of the pouches so that the pouches may be filled with articles to be packaged.
When a package is sealed, it typically has protruding gabled ends adjacent the seals which must be tucked in at the sides and/or folded against the package to complete the packaging process. Tucking and folding the gables is typically accomplished by various mechanical arrangements which require precise timing. During the tucking step, it is critical that any wrinkling or crumpling of the material around the gables be avoided for the reasons set forth above and because any such wrinkling or crumpling, or any folding of the material at locations other than at the desired gable fold lines, may produce a defective seal resulting in leaks and/or contamination of the packaged articles.
There have been numerous advances directed to tucking or folding the sides of sealed packages. U.S. Pat. No. 5,191,750 discloses a sealing apparatus whereby tubular wrapping material is sealed by a closable cross sealing jaw and side folding rods positioned upstream from the cross sealing jaw are used to create folds or tucks in the sides of the wrapping material before the material is sealed. U.S. Pat. No. 2,722,094 discloses a wrapping and folding machine for covering packets with a wrapping material and carrying out the final folding and closing operations. After the package has been substantially wrapped, two tuckers are moved toward one another from opposite sides of the package so as to tuck in the wrapping material at the two rearward corners of the package. A downwardly depending folding flange at one end of the top folding plate turns down the upper rearwardly extending part of the wrapping material and the remaining rearward extension of the wrapping material is turned upwards by engagement with a fixed plate or bar at the end of the machine for completing the wrapping of the packet. U.S. Pat. No. 3,457,692 discloses a gable end folding method whereby the gables are folded by providing a line of sealed packages in end-to-end relationship and sequentially reducing the distance between the packages so that the gables engage one another and are constrained to fold.
Another problem associated with sealing machinery relates to the reduction in the downstream speed of the wrapping material when seals are formed between the articles. This reduction in speed occurs when the wrapping material is collapsed between successive articles to form a seal whereby the distance between the successive articles is decreased. The speed of the wrapping material must be reduced or the packaging material will stretch and/or tear, resulting in the formation of a defective package. Another benefit of reducing the speed of the wrapping material is that the packages are wrapped more tightly. These more tightly wrapped packages use less film and are more cosmetically appealing. The reduction in the speed of the wrapping material during sealing is not a problem in sealing machinery having only a single sealing jaw because only one seal and cut may be made at a time so that a package being sealed and cut can change velocity without restraint. However, whenever two or more sealing jaws are simultaneously in contact with the wrapping material, and where these multiple sealing jaws are operated at a constant velocity, the closing action of the sealing jaws pulls excess film from downstream which results in an undesirable jerking motion of the wrapping material. U.S. Pat. No. 5,433,632 discloses an apparatus whereby the speed of the articles to be packaged and the wrapping material is adjusted at a heat sealing station in order to compensate for the reduction in velocity due to deformation of the material between the articles. In other words, the articles to be packaged and the wrapping material are decelerated during the sealing and cutting operation in order to compensate for the reduction in the length of the material due to the formation of gables. The sealed and severed packages together with the packaged articles are then accelerated to the incoming web speed before exiting the sealing station of the machine. Although the '632 patent responds to the reduction in speed of the wrapping material, it would be preferable to slow down the material in stages to reduce the stress on the material.
U.S. Pat. No. 2,718,105 discloses a multi-stage sealing machine for sealing bag-like containers. A roll of flexible wrapping material is passed downstream to a first sealing station which seals the bottom sides of the container and forms a trough-like configuration in the bottom thereof. A second sealing station seals the sides of the container and a further station separates the cartons from the web. After the containers have been sealed along the sides, the containers pass downstream to a severing roll. The severing roll cuts the individual packages from the web and kicks the individual packages off at the ends where they are collected. The severing rolls rotate at a greater peripheral speed then the side sealing rolls so that the severed packages are given a thrust or kick and fall away from the end of the machine.
Despite these and other efforts in the art, there are needs for still further improvement.